On Oct. 8, United opened its maintenance base at San Francisco International Airport (SFO) up to airline employees and their families for the carrier's annual SFO Family Day. This year was special, though, as the airline celebrated the end of an era, saying goodbye to the Boeing 747 fleet. [envira-gallery id="16323"] At the event, two 747-400 aircraft were on display — N118UA and N119UA — each of which had lines circling around the ramp area for those eager to get onboard.…